Slow in what manner? Internet is slow, Firefox itself is slow, etc? Have you tried to Reset Firefox? Refresh Firefox - reset add-ons and settings

hello, for more information on how to speed things up please also refer to Quick fixes if your Firefox slows down & keep your plugins updated!

You can also try to disable IPv6 in Firefox:

• http://kb.mozillazine.org/Error_loading_websites#IPv6

I have the same problem. but only started I would say about 2 months ago. before firefox was ok. I never compared it to another browser until just couple weeks ago. I am using crome now and wow what a difference. I tried everything and its still slow. reset it. reinstall it. disable all the add ons. clear cash. everything with no luck.